Various systems have been developed to filter water and wastewater. Typical filter systems include but are not limited to an upflow filter, a downflow filter, a combined upflow filter and a downflow filter and multiple downflow filters connected in series. The term upflow filter is given to a filter in which the liquid or influent to be filtered is directed in an upward path to remove impurities. Conversely, a downflow filter is a filter in which the influent is directed in a downward path to remove impurities. In a combined upflow/downflow filter, influent is directed upwardly through the upflow filter to remove a predetermined percentage of the impurities in the influent and then the influent is directed downwardly through the downflow filter to remove the remaining impurities to within an acceptable limit. In this type of system, it is common for the upflow filter and downflow filter to include one or more layers of filter media supported by one or more gravel support layers. Gravel support layers are necessary for certain filter systems to prevent clogging of the underdrain. For example, one common type of underdrain includes a plurality of underdrain blocks arranged in parallel rows across the bottom of the filter. The underdrain blocks act to direct and receive fluids including influent, effluent and air during operation of the filter system. The underdrain blocks typically include multiple large apertures through which the fluids are directed and received. The apertures are of such a size that the filter media can pass therethrough and clog the underdrain block. This of course is disadvantageous. One solution has been the use of one or more gravel support layers to support the filter media. The gravel is larger than the openings in the underdrain block and, therefore, does not pass therethrough.
However, gravel support layers have a number of disadvantages. Specifically, gravel support layers are expensive and time consuming to install. Further, gravel support layers consume a significant portion of the filter chamber thus reducing the filtering capacity of the bed. Also, gravel support layers are subject to being upset when uncontrolled air enters the filter bed due to improper installation of the air system or operator error. Moreover, in filter beds using granular activated carbon such must occasionally be removed from the filter and placed in a reactivation furnace. During removal of the granular activated carbon, the gravel becomes intermixed and is deposited in the reactivation furnace. At the extreme temperatures necessary to reactivate the granular activated carbon the gravel can explode damaging the furnace.
To overcome the disadvantages of gravel support layers, porous plates have been used with underdrain blocks. The porous plates obviate the need for the gravel support layers because they prevent the filter media from passing through the apertures in the underdrain block. Typically, porous plates have been fastened directly to the underdrain block with screws or bolts. This conventional means of securing the porous plate to the underdrain block has significant drawbacks. These conventional fasteners increase the cost of the system from both a materials and labor stand point. Further, if the porous plate needs to be replaced a laborer would be required to removal all of the numerous fasteners before such could be accomplished. Moreover, conventional fasteners could damage the porous plate requiring its removal. In addition, a direct connection of the porous plate to the underdrain block without sufficient offset would likely lead to maldistribution of the fluid.
To overcome the disadvantages of prior underdrain systems including but not limited to the disadvantages attendant securing a porous plate to an underdrain block with conventional fasteners Roberts Water Technologies introduced the novel and unobvious INFINITY™ continuous lateral underdrain. This underdrain is prior art to the subject patent application as it was sold or offered for sale more than a year prior to the filing date of the subject patent application. This underdrain is advertised on the World Wide Web at www.robertsfiltergroup.com. While the INFINITY™ underdrain is a significant improvement over previously developed underdrains, the present invention is yet a further substantial improvement over the INFINITY™ underdrain. Specifically, one aspect of the present invention includes a novel and unobvious means for permitting a porous plate to be readily removed from a supporting structure allowing replacement thereof. A significant advantage to this aspect of the invention is that the porous plate can be removed from the supporting structure readily without damaging the major components of the underdrain.
Another significant disadvantage of prior developments is that an existing underdrain could not be satisfactorily retrofitted with a porous plate thereby obviating the need for one or more gravel support layers. Further, prior developments lacked the ability to readily retrofit numerous different types of underdrains with a porous plate to thereby obviate the need for one or more gravel support layers.
Prior fluid distribution systems included means for distributing air to a filter bed having one or more layers of media during washing of the filter bed. This is commonly referred to as air scouring. Air scouring has been determined to be an important process in cleaning filter beds. A number of existing underdrain systems are designed such that liquids and gases flow through common conduits. Such underdrain systems have significant drawbacks. Specifically, because of the conflict between the flow rates of liquids and gases, upper limits must unnecessarily be imposed minimizing the flexibility in setting different ranges of flow rates for liquids and gases. Further, common discharge passages for liquids and gases result in uneven discharge of the air bubbles resulting in undesirable maldistribution. To overcome the disadvantages of prior underdrain systems including but not limited to the disadvantages attendant common liquid and gas conduits, Roberts Water Technologies introduced the novel and unobvious ARIES® managed air systems. This managed air system is advertised on the World Wide Web at www.robertsfiltergroup.com. and disclosed in U.S. Pat. Nos. 5,535,202 and 5,673,481. While the ARIES® managed air system is a significant improvement over previously developed air scour systems, the present invention is yet a further substantial improvement as will be readily recognized by those skilled in the art.
Some previously known air scour systems have also suffered from the disadvantage of maldistribution owing to incomplete evacuation of water from the air conduit. The problem of incomplete evacuation of water is often experienced where the air conduit has not been installed correctly. One example, is an unlevel installation of the air conduit. In such circumstances, the exit or discharge openings on the low side of the air conduit often remain blocked by water preventing proper distribution of air to the filter bed to adequately clean the same.
Previously known combined air and liquid distribution systems utilizing shared conduits have experienced uncontrolled releases of air which can lead to significant problems. Specifically, systems using shared conduits are likely to experience rapid introduction of air or water flow. This rapid introduction of flow can create a wave action resulting in fluctuation of the interfaces which can expose the water metering orifices to air flow resulting in gross maldistribution.